I pursue this Mentored Research Scientist Development Award (K01) as a training mechanism to facilitate my transition towards an independent research career in HIV intervention science. My current training is limited to individual-level secondary HIV prevention/treatment interventions in clinical care settings, and is insufficient to address the sociostructural contexts (e.g., stigma/discrimination, inadequate cultural competency among providers, negative community environments, lack of protective policy/laws1-4) limiting the promise of HIV Treatment as Prevention (TasP) efforts by NIH/UNAIDS to curb the HIV epidemic via effective antiretroviral therapies. Specifically, the K01 will support this transition by: 1) acquiring theoretical and statistical skills for the developmen, implementation, and evaluation of sociostructural-level interventions, 2) provide hands-on training in health promotion research and ethical considerations with key populations, such as men who have sex with men (MSM), in low/middle income countries (LMIC) where TasP efforts are most limited,5,6 and 3) develop the necessary collaborations and research infrastructure to enable academic independence as an NIH-funded investigator. These training aims will be accomplished through a combination of didactic courses, workshops, integration into prominent HIV prevention science networks, hands-on research and mentored training in sociostructural assessment and intervention methods with key populations in LMIC settings. Research and Environment. The proposed research will be conducted as an independent study, adjunct to an existing NIDA-funded R01 (HIV case finding and genetic transmission networks among MSM in Tijuana; PI: Patterson; 1R01DA037811-01), in order to capitalize on its available research infrastructure and identification of HIV+ MSM in a LMIC setting. The US-Mexico border is facing a burgeoning HIV epidemic concentrated among key populations affected by HIV and substance use globally (i.e., MSM, persons who inject drugs, and sex workers).7 While current TasP efforts have sought to improve individual HIV treatment behaviors in these key populations (e.g., HIV testing, linkage/retention in care, ART adherence), progress will remain stunted until there is sufficient knowledge and capacity to address current sociostructural barriers.5,8,9 The need for more favorable sociostructural climates in HIV treatment is especially true for these key populations for whom HIV rates continue to escalate.6,10 The proposed research will provide me with the training necessary to address these gaps as an HIV interventionist. I will use mixed methods to identify key sociostructural determinants of HIV treatment success in HIV+ MSM 12-months post-diagnosis. This information will be used to adapt/develop sociostructural intervention strategies that can be implemented, and piloted for feasibility/acceptability. This training will uniquely position me as one of a few sociostructural interventionist focused on advancing the promise of TasP, and the only multi-level secondary prevention interventionist within my Division at UCSD.